A major research goal of this project is to understand the role of the extracellular matrix in metastasis and invasion, focusing currently on identifying integrin-mediated signaling pathways that regulate tumor invadopodia assembly, their function in proteolytic degradation, and tumor cell invasion. A fundamental question in cancer biology is the relationship of the local matrix environment to cancer progression. For example, a common feature of advanced carcinomas is the induction of a dense collagenous matrix surrounding tumors during the process of desmoplasia. However, whether this increase in collagen is protective against tumor expansion or actually contributes to cancer pathogenesis is not known. We have been characterizing in depth the effects of extracellular matrix on invadopodia formation, testing a current hypothesis that increased matrix density contributes to cancer pathogenesis. We have been developing two different systems to test this concept: (a) evaluating effects of endogenous desmoplastic 3D matrix from human tumors on invadopodia formation, and (b) using in vitro systems to model this dense collagenous matrix in order to identify novel molecular mechanisms regulating invadopodia formation. We have developed methods to test the capacity of intact, cell-free 3D human tumor matrix on the ability of tumor cells to form invadopodia. This new protocol uses extracted extracellular matrix from cryostat sections of human breast and pancreatic cancers versus normal adjacent tissue. Its development required solving various technical problems to successfully produce intact, cell-free 3D human tissue matrix suitable for testing cell-matrix interactions and performing immunofluorescence analyses. We have also developed a novel in vitro high-density fibrillar collagen (HDFC) matrix to mimic the dense fibrillar collagen of advanced tumors. HDFC was found to be a potent inducer of invadopodia in a variety of cell lines. In human carcinoma cells, HDFC matrix induced invadopodia via a specific integrin signaling pathway that did not require growth factors or even altered gene and protein expression. In contrast, phosphoproteomics identified major changes in a complex phospho-signaling network, with kindlin2 serine phosphorylation as a key regulatory element. This kindlin2-dependent signal transduction network was required for efficient induction of invadopodia on dense fibrillar collagen and for local proteolytic degradation of collagen. Dominant-negative mutants of kindlin2 inhibited invadopodia formation in cells invading HDFC, whereas mutations to generate phosphomimetics induced increased numbers of invadopodia-forming cells in cells invading globular collagen matrix (which normally induces few invadopodia). Expression of exogenous kindlin2 rescued invadopodia formation in cells with depleted endogenous kindlin2, but expression of exogenous dominant-negative mutants did not. These findings represent the first identification of a novel phospho-signaling mechanism regulating cell surface invadopodia via kindlin2 for local proteolytic remodeling of the ECM. We are also evaluating how changes in 3D matrix rigidity alone may affect tumor cell migration in collaboration with Daniel Blair in the Institute for Soft Matter at Georgetown University. Using a custom-built confocal microscope-rheometer, we will image 3D cell migration while dynamically altering matrix rigidity. This unique system will potentially permit the selective modification of 3D matrix stiffness without affecting other physical or chemical parameters. Interactions at the cell surface are likely to play important roles in many diseases. We have been involved in a long-term collaboration with Dr. Subhash Dhawan in CBER, FDA to characterize cell-surface and extracellular interactions involved in the pathogenesis of infectious diseases. We have been exploring a novel role for heme oxygenase-1 (HO-1) in host immune response against viral infections. Treatment of human monocyte-derived macrophages with lipopolysaccharide (LPS) strongly induced expression of HO-1 and inhibited HIV-1 entry and replication. This HO-1 induction was accompanied by enhanced production of several macrophage chemokines. This study identifies a novel role for HO-1 in modulating host immune responses to inhibit HIV infection of macrophages. This approach was then extended to evaluate the effects of HO-1 induction by hemin on a prostate tumor cell line; it inhibited cell proliferation rate and susceptibility of the cells to retroviral infection. We have been evaluating efficacy of hemin treatment of human macrophages and its associated HO-1 induction for suppression of infectivity by other viruses, such as West Nile virus, as well as by the protozoan parasite Leishmania. We suggest that HO-1 induction via hemin, an FDA approved drug, might provide a potential host-defense therapeutic strategy against a variety of pathogens.